Examples of curved reflectors and lenses that are both commonly used as collimating elements in high-gain, narrow beam microwave antennas as described in the following U.S. Patents, the disclosure of which are incorporated herein by reference:
U.S. Pat. No. 4,721,966 issued to Daniel McGrath; PA1 U.S. Pat. No. 4,381,509 issued to Walter Rotman; PA1 U.S. Pat. No. 4,131,892 issued to Robert Munson et al; PA1 U.S. Pat. No. 4,263,598 issued to Ernest Bella et al; and PA1 U.S. Pat. No. 4,329,689 issued to Jones Yee.
The microwave lens systems of the above-cited references may be used in a number of different applications including communications and direction finding. The choice between a reflector or lens for a given application depends upon many factors. For example, the Rotman lens is considered the optimum beamformer for producing time-delay steered beams over wide angles, but its requirement of a curved back face prohibits application to some problems, most notably those requiring large planar arrays.
Alternatives to the Rotman lens include curved wide-angle lenses and planar lenses. These lens systems are known in the art, and each possess advantages and disadvantages. For example, a planar lens (with a planar front surface which is parallel to a planar back surface) is incapable of wide-angle scanning, because the elements of the back face are normally placed directly behind the front face elements. Curved wide-angle lenses are heavy and expensive to build.
The basic microstrip constrained lens was described in U.S. Pat. No. 4,721,966, "Planar Three-Dimensional Constrained Lens for Wide-Angle Scanning." That patent described the design of a wide-angle microwave lens. It was an improvement over previous microwave lenses, such as the Rotman lens, which were limited to scanning in one plane only.
The present invention is a modification to the lens described in U.S. Pat. No. 4,721,966. That earlier lens used a pin coupler to route microwave energy from one side of the lens to the other The new version of the present invention uses a slot coupler. The efficiency of power transfer through the two lens systems in experiments was found to be approximately the same. Since the slot coupler does not require drilling a hole for a pin or soldering it to the open transmission line ends, it is much easier to build, and therefore less expensive. It is very lightweight, due to its construction from a circuit board.
From the foregoing discussion, it is apparent that a lightweight scanning lens antenna which uses a planar lens, yet is capable of performing wide-angle scanning would be a welcome addition to the art of beamforming lens design. The present invention is intended to provide a new lightweight design which uses a planar lens, yet is capable of wide-angle scanning